The invention relates generally to electromagnetic clutches and more specifically to an electromagnetic clutch having a solenoid activated ball ramp operator.
Clutches which are activated or energized by electromagnetic coils are extraordinarily common components in rotary power transmission systems, both in stationary applications and in motor vehicles. Such electromagnetic clutches may be broadly characterized by whether they provide on-off energy transfer or modulating energy transfer. In the case of the former, dog clutches which may include auxiliary synchronizing devices are utilized whereas in the latter, friction clutch packs having a plurality of interleaved friction plates or discs are utilized. In either case, an electromagnetic operator which translates or compresses components of the clutch upon energization activates the clutch and upon deenergization deactivates or relaxes the clutch.
One of the design and operational characteristics of electromagnetic clutches which receives significant engineering attention is power consumption. It is desirable, especially in motor vehicles, to design and utilize a clutch having low power consumption. Low power consumption is desirable in and of itself but it also reduces the heat generated by the coil and lower power consumption can reduce the need for cooling the coil, can improve the service life of the coil and is therefore overall a desirable design goal.
A design which exhibits low power consumption is generally referred to as a cam or ball ramp actuated clutch. Here, a pair of opposed plates having caming members or opposed arcuate recesses which receive balls or roller bearings separate upon relative rotation caused by drag resulting from energization of the electromagnetic coil. Such separation compresses an adjacent friction clutch pack which transfers drive energy or torque across the friction clutch pack. Such a device is disclosed in conjunction with a transfer case in U.S. Pat. No. 4,989,686, co-owned by the Assignee herein.